The present disclosure relates to nerve stimulation and recording systems. In particular, it relates to electrodes adapted to stimulate nerves or record neurogenic responses.
In many invasive medical procedures, steps are taken to preserve healthy surrounding tissues while performing the procedure on a target tissue. In one example, in surgeries involving the head and neck, a surgeon must guard against unintentional damage to surrounding nerves while excising other tissue, such as a tumor. This damage may result from direct trauma (e.g. an incision) or “blind” trauma, such as stretching, torsion, compression, ischemia, thermal damage, electrical damage, or other surgical manipulations. Blind damage is of particular concern because the damage may be cumulative over the course of the surgery but may not be recognizable by the surgeon during the surgery.
One conventional technique of preserving the nerve includes the surgeon periodically applying a stimulation probe at the nerve and simultaneously measuring the neurogenic response from an associated innervated muscle via electromyography or other techniques. Accordingly, each time the surgeon desires to check the health or integrity of the nerve, the surgeon will maneuver the probe to contact the nerve, and apply the stimulation signal. After measuring and observing the response to the stimulus, the surgeon removes the probe from contact with the nerve.
Unfortunately, this conventional technique can lead to many inconsistencies. For example, it is difficult to establish accurate information about the response of an unimpaired nerve because the stimulation probe is placed in a slightly different location each time it is applied, resulting in a slightly different stimulus to the nerve. This contact variability in applying the stimulus leads to a slightly different response pattern. Accordingly, the slightly different locations of stimulation tend to cloud ascertainment of a normal or typical response of the innervated muscle (when the nerve is not impaired) and also cloud identification of a response signal that corresponds to an impairment or disturbance of the nerve. Moreover, because the stimulation probe is applied intermittently, there is no assurance whether the response signal is being measured at the time that the nerve is being impaired or being measured at the time the nerve is not being impaired.
Accordingly, the conventional techniques used during a medical procedure to monitor the health of a nerve fall short of the consistency and accuracy that would be desirable to reliably ascertain the integrity of the nerve during surgery.